The present invention relates to devices pre-loaded with a medicine and intended to automatically administer a pre-determined dose of a liquid medicine by means of an intramuscular, subcutaneous or transdermal injection. In particular, the present invention incorporates a number of important improvements and features as compared to the prior art, including enhanced functionality, convenience, safety and versatility. The present invention also provides a means for quickly administering a pre-determined dose of medication when a need for rapid emergency treatment arises. The present invention may be embodied in a device that can be easily, safely and conveniently carried on the person. The present invention allows a single embodiment that may administer a liquid medicine alone or, alternatively, allow a liquid solvent to automatically mix with a dry medicine upon actuation of the device and concurrent with the injection process. The preferred embodiment automatically renders itself safe for disposal after use and eliminates the risk of injury to others through inadvertent contact with the used hypodermic needle. The recipient before, during, or after the injection, need not even see the hypodermic needle.
The use of automatic injection devices has been primarily reserved to emergency, life-sustaining situations. Additional applications for the present invention would be instances where the anatomical site of the injection, such as the penis, make the functional and psychological benefits associated with the use of such a device worth the added cost as compared to the conventional syringes.
There are numerous embodiments of automatic injection apparatuses in the prior art, e.g. Wyrick, U.S. Pat. No. 5,665,071; Schmitz, U.S. Pat. No. 5,620,421; and Wilmot, U.S. Pat. No. 5,295,965. None of the prior art patents provide all of the benefits of the present invention, however.
The present invention pertains to an automatic injection apparatus which injects a single, pre-measured dose of stored medicine intramuscularly or transdermally, and which automatically retracts the hypodermic needle into the device after the injection is completed. In the preferred embodiment, the medicine may comprise either a preprepared liquid medicine, a liquid solute that is forced through a dry drug chamber where a soluble medicine is mixed with the solute and carried in solution into the recipient, or a combination of a liquid medicine that also serves as a solute for a dry drug that mixes upon injection.
The preferred embodiment resembles a permanent marker pen. It has an actuation end and a needle end. For the purposes of this application, the actuation end of the device will be referred to as the proximal end of the device and the needle end will be referred to as the distal end. A removable cap preferably covers the proximal end of the device to protect against accidental actuation. The user presses the distal end of the device onto the desired injection site and presses the actuation button. This releases the plunger and syringe combination from its temporary engagement with the housing. The plunger and syringe combination is then forced away from the proximal end of the housing by a energized driver spring. The driver spring propels the plunger and syringe combination forward through the bore of the housing until the hypodermic needle exits the housing, and enters the recipient""s tissue. During this movement, a return spring positioned between the syringe assembly and the fixed, distal end of the housing becomes compressed and energized. Once the plunger and syringe combination comes to rest against the impact damper pad at the distal end of the housing, the syringe assembly remains stationary and the plunger begins to move axially forward relative to the syringe. As the plunger moves forward, the pressure within the liquid within the syringe begins to rise rapidly until it reaches a critical threshold pressure. Upon reaching the threshold pressure, a rigid disk separating the first liquid chamber from the second dry drug chamber disengages from a circumferential seal holding it into place relative to the syringe. Once separated from the circumferential seal, the disk moves forward until it comes to rest against a retaining surface in the dry drug chamber and the liquid flows through apertures around the disk and into the dry drug chamber.
If the dry drug chamber contains a dry medicine, the dry medicine is drawn into solution by the liquid as the plunger continues its forward movement and the liquid is forced through the dry drug compartment and into the entrance to the hypodermic needle. Otherwise, the liquid medicine flows through the same chamber and continues on into the recipient. When the liquid is discharged, the coupling that engages the driver spring and the plunger comes into contact with a splitter which disengages the driver spring from the plunger. Without the influence of the driver spring upon the plunger and syringe combination, the energized return spring forces the plunger and syringe combination to retreat rearward towards the proximal end of the device until the hypodermic needle is fully retracted into the housing.
In general, the preferred embodiment comprises a housing having a cavity and a proximal and a distal end. A syringe assembly is located within the housing cavity, and the syringe assembly further comprises a first chamber for holding a liquid; a second chamber for holding a dry medicine (the second chamber disposed distally to the first chamber); a disk releasably sealing the first chamber from the second chamber; a needle, (the needle disposed distally of the second chamber); a plunger having a plunger shaft disposed proximally; and, at least one aperture in the wall of the second chamber allowing liquid communication between the portion of the second chamber proximal to the released disk and the portion of the second chamber distal to the released disk, so that the liquid flows through the second chamber before being forced through the needle. The plunger operates to force the liquid from the first chamber into the second chamber.
A driver spring is located within the housing. The driver spring engages the plunger shaft, and operates, when released, to inject the needle and displace the liquid from the first chamber, through the second chamber and through the needle. A spring-top-plunger coupling engages the plunger shaft and the driver spring. A splitter is attached to the housing distally to the spring-to-plunger coupling. The splitter has a surface for engaging the spring-to-plunger coupling and forcing the spring-to-plunger coupling to disengage from the plunger shaft, thereby disengaging the driver spring from the syringe assembly.
The driver spring is disengaged by opening of the spring-to-plunger coupling. The plunger shaft has a circumferential groove; and, the spring-to-plunger coupling has a plurality of axial slits and a radial lip for releasably engaging the circumferential groove. Thus, the radial lip disengages from the circumferential groove as the spring-to-plunger coupling engages the splitter, and the spring-to-plunger coupling is forced open.
The plunger shaft has at least two compressible barbs connected to its proximal end. An actuation rod is axially moveable within the housing. The rod has an interior bore sized to receive the barbs in their compressed state. The housing has a detent sized to engage the barbs in their uncompressed state and prevent the distal movement of the plunger shaft until the barbs are compressed.
A return spring is disposed between the housing and the syringe assembly, and urges the syringe assembly proximally.
The preferred embodiment has a flexible septum disposed proximally to the proximal end of the needle and sealing the needle from the second chamber, so that liquid pressure in the second chamber causes the septum to deflect distally until it is penetrated by the proximal end of the needle.